package leetcode.editor.cn;
//给你一棵二叉树的根节点 root ，翻转这棵二叉树，并返回其根节点。 
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// 示例 1： 
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//输入：root = [4,2,7,1,3,6,9]
//输出：[4,7,2,9,6,3,1]
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// 示例 2： 
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//输入：root = [2,1,3]
//输出：[2,3,1]
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// 示例 3： 
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//输入：root = []
//输出：[]
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// 提示： 
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// 树中节点数目范围在 [0, 100] 内 
// -100 <= Node.val <= 100 
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// Related Topics 树 深度优先搜索 广度优先搜索 二叉树 
// 👍 1552 👎 0


//leetcode submit region begin(Prohibit modification and deletion)

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 * int val;
 * TreeNode left;
 * TreeNode right;
 * TreeNode() {}
 * TreeNode(int val) { this.val = val; }
 * TreeNode(int val, TreeNode left, TreeNode right) {
 * this.val = val;
 * this.left = left;
 * this.right = right;
 * }
 * }
 */
class Solution78 {

    /**
     * 先管当前节点，后续递归遍历子节点
     * @param root
     * @return
     */
    public TreeNode invertTree(TreeNode root) {
        if (root == null) {
            return null;
        }
        TreeNode left = root.left;
        TreeNode right = root.right;
        root.left = right;
        root.right = left;
        invertTree(left);
        invertTree(right);
        return root;
    }

    /**
     * 先管子节点，后续处理当前节点
     * @param root
     * @return
     */
    public TreeNode invertTree1(TreeNode root) {
        if (root == null) {
            return null;
        }
        TreeNode left = invertTree(root.left);
        TreeNode right = invertTree(root.right);
        root.right = left;
        root.left = right;

        return root;
    }

    public class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode() {
        }

        TreeNode(int val) {
            this.val = val;
        }

        TreeNode(int val, TreeNode left, TreeNode right) {
            this.val = val;
            this.left = left;
            this.right = right;
        }
    }
}
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